showing overheating but not overheating
11-20-2017, 07:39 AM
#1
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showing overheating but not overheating
my 99 honda lx 4 cyl. goes to the H when sitting in traffic or at redlight but goes down to normal temp when i am driving again. i already changed the fan which was bad and it was fine for a week but started back doing it. what should i check next?
11-20-2017, 08:20 AM
#2
Re: showing overheating but not overheating
Seems like your fan is not getting the signal to turn on. Check that presumption first.
With the Accord in park, turn the temperature dial on the climate control to full heat and turn the blower off. Start the car, pop the hood, and hold the idle between 2000 and 3000. It'd be helpful if you have a DTC reader for this step; with this tool you will know the exact coolant temperature in real time. After the engine coolant heats to ~199°F, the fan is triggered. In the absence of a DTC reader, you'll just have to WAG it and presume that if, after 5mins of idle the fans do not activate, you have a problem upstream.
Begin by eliminating the fan fuse and fan relay--the former is in the fuse box under the drivers seat, and the latter in the engine compartment. Test the fuse with a continuity tester; or test both by swapping with an identical known-good part. When the fuse tests OK--and it will, 'cause fuses rarely go bad--check the wiring to the fan by jumping across "1" and "2" contacts in the relay socket--the fan should come on.
- If the fan does not come on, remove the jumper, turn the ignition switch to Accessory, and use a multimeter to check for 12v between "3" contact and ground. If you have power, then fan relay is suspect.
- If the fan comes on, then perform a continuity check of the wire that runs from the engine compartment fuse box to the fan connector--look for continuity between the "2" contacts in both the relay socket and the fan connector, then check for continuity between the "1" contact the fan connector and ground. If both show continuity AND the fan works, then the problem is upstream in one of the temperature sensors.
Check the radiator fan switch (RFS) first, which is located in the thermostat cover. The coolant temperature sensor (CTS) may also play a role here, but I am not certain (Honda techs?). While you can test both with a multimeter to determine if their output at a given temperature matches what is recorded in the service manual, it's easier to simply swap in a known-good RFS and CTS--neither part is a particularly expensive. Try the RFS first.
Advisory 1: Honda's tend to be particular about certain parts being OEM, and sensors are among them. If you replace your CTS, I recommend you use an OEM part no 37870-PK2-015.
Advisory 2: Perform a proper engine coolant bleed procedure if you replace either sensor--you risk messing up your idle (believe it or not) if you skip this perfunctory step. There are plenty of YouTube videos that detail the process.
Fix this problem. You risk overheating your engine otherwise. I understand that is bad.
With the Accord in park, turn the temperature dial on the climate control to full heat and turn the blower off. Start the car, pop the hood, and hold the idle between 2000 and 3000. It'd be helpful if you have a DTC reader for this step; with this tool you will know the exact coolant temperature in real time. After the engine coolant heats to ~199°F, the fan is triggered. In the absence of a DTC reader, you'll just have to WAG it and presume that if, after 5mins of idle the fans do not activate, you have a problem upstream.
Begin by eliminating the fan fuse and fan relay--the former is in the fuse box under the drivers seat, and the latter in the engine compartment. Test the fuse with a continuity tester; or test both by swapping with an identical known-good part. When the fuse tests OK--and it will, 'cause fuses rarely go bad--check the wiring to the fan by jumping across "1" and "2" contacts in the relay socket--the fan should come on.
- If the fan does not come on, remove the jumper, turn the ignition switch to Accessory, and use a multimeter to check for 12v between "3" contact and ground. If you have power, then fan relay is suspect.
- If the fan comes on, then perform a continuity check of the wire that runs from the engine compartment fuse box to the fan connector--look for continuity between the "2" contacts in both the relay socket and the fan connector, then check for continuity between the "1" contact the fan connector and ground. If both show continuity AND the fan works, then the problem is upstream in one of the temperature sensors.
Check the radiator fan switch (RFS) first, which is located in the thermostat cover. The coolant temperature sensor (CTS) may also play a role here, but I am not certain (Honda techs?). While you can test both with a multimeter to determine if their output at a given temperature matches what is recorded in the service manual, it's easier to simply swap in a known-good RFS and CTS--neither part is a particularly expensive. Try the RFS first.
Advisory 1: Honda's tend to be particular about certain parts being OEM, and sensors are among them. If you replace your CTS, I recommend you use an OEM part no 37870-PK2-015.
Advisory 2: Perform a proper engine coolant bleed procedure if you replace either sensor--you risk messing up your idle (believe it or not) if you skip this perfunctory step. There are plenty of YouTube videos that detail the process.
Fix this problem. You risk overheating your engine otherwise. I understand that is bad.
Last edited by lothian; 11-21-2017 at 07:40 PM.
11-20-2017, 09:11 AM
#4
Re: showing overheating but not overheating
Do some simple checks/tests first.
1. Check your coolant level in the radiator and the reservoir.
2. Turn on the A/C, does both cooling fans run? Both should run with the A/C on.
3. Locate the radiator fan switch at the thermostat housing (where the lower radiator hose runs to). Unplug the 2P connector and jump the disconnected wire harness connector with a wire or small paper clip. Turn the ignition ON, both fan should run. If both fans run, the relay and fuse are good. Issue may be the fan switch if both fans run from this check.
1. Check your coolant level in the radiator and the reservoir.
2. Turn on the A/C, does both cooling fans run? Both should run with the A/C on.
3. Locate the radiator fan switch at the thermostat housing (where the lower radiator hose runs to). Unplug the 2P connector and jump the disconnected wire harness connector with a wire or small paper clip. Turn the ignition ON, both fan should run. If both fans run, the relay and fuse are good. Issue may be the fan switch if both fans run from this check.
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